package main

import (
	"bytes"
	"fmt"
	"io"
	"os"
)

var b os.File

func main() {

	var w io.Writer = os.Stdout
	f := w.(*os.File) // success: f == os.Stdout
	fmt.Errorf("w:%T\n", w)
	fmt.Printf("f:%T\n", f)

	c := b.(io.Writer)

}
